Add a better dev console via script/console

This switches the default IRB-based console over to pry. It also defines a helper method `repo` which is a `Rugged::Repository` instance pointed to the local rugged git clone you're running the console from. This is so you can get started right away with testing whatever changes you're working on.

![rugged__ruby__10429](https://f.cloud.github.com/assets/11571/750837/814aa3e6-e4db-11e2-8c42-b53dba7b3407.png)

I snuck in a `script/bootstrap` script as well which makes it a little easier to install the dev bundle.